Session
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2022-05-15 10:57:37
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Session
session：会话，是棵树段访问服务器服务器给客户端响应，直到客户端断开服务器为止的活动为止，被称为会话
会话的好处在于让我们更加方便的取到用户的信息
会话的创建
admin.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'admin.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
This is my JSP page.
<%=(String)session.getAttribute("a") %>
<%=(String)session.getAttribute("b") %>
<br>
</body>
</html>
index.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'index.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<form action="sessionServlet" method="post">
姓名： <input type="text" name="name"><br> 密码： <input
type="text" name="password"><br> <br> <input
type="submit" value="注册"><br>
</form>
<br>
</body>
</html>
tiaozhuan.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'denglu.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
denglu.jsp
<%=request.getParameter("name")%>
<%=(String)session.getAttribute("a") %>
<%=(String)session.getAttribute("b") %>
<a href="student/admin.jsp">进入admin</a>
<br>
</body>
</html>
sessionServlet
package session;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class sessionServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String name=request.getParameter("name");
String password=request.getParameter("password");
//先在数据库查询到信息并登录成功
//===================session======================
HttpSession session=request.getSession();
session.setAttribute("a", name);
session.setAttribute("b", password);
request.getRequestDispatcher("student/tiaozhuan.jsp").forward(request, response);
}
}
Session的消失
session的消失有两种方式，一种是Tomcat自定义的时间，另一种是关闭浏览器，我们也可以用session.setMaxInactiveInterval(30);方法来改变session消失时的时间
另外，session.setMaxInactiveInterval(30);的时间单位为秒，tomcat的设置是30分钟，用此方法设置session的消失时间的时候，如果失职的时间比30分钟长，那么session的消失时间仍旧为30分钟，两个值取时间短的，Tomcat的默认消失时间在web.xml文件下，如下：
<session-config>
<session-timeout>30</session-timeout>
</session-config>
Session立即消失
session中有方法session.invalidate();方法，可以让session立即消失
写一个退出的servelt
LoginServlet
package session;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class loginOffServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
/**
* session立即消失
*/
HttpSession session = request.getSession();
session.invalidate();// 立即退出，session立即消失
request.getRequestDispatcher("index.jsp").forward(request, response);
}
}
在jsp文件写<a href="loginOffServlet">退出</a>，在页面中点击退出session立即消失，并返回登录页面
页面访问权限控制
在admin页面加入代码，当用户的session失效时提示他重新登录
<%
Object obj=session.getAttribute("name");
if(obj!=null){
request.setAttribute("tishi", "请登录");
request.getRequestDispatcher("../student/index.jsp").forward(request, response);
}
%>
然后跳转回登录页面，但是退出登录不要让提示信息显示出来
<%String tishi=(String)request.getAttribute("tishi");
if(tishi!=null){%>
<%=tishi %>
<% } %>
另外，request.getRequestDispatcher("…/student/index.jsp").forward(request, response);方法带参跳转，但是地址栏不变，叫做服务器内部跳转
response.sendRedirect("");方法不带参跳转，但是地址栏会变化，叫做浏览器跳转
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